High-tech device dramatically speeds
recovery from hypothermia

Stanford researchers have developed a
high-tech solution that dramatically reduces the
recovery time for the mild hypothermia that often
accompanies major surgery. A device called the
Thermo-STAT, which fits over the hand and
forearm, also holds promise for the treatment of
more severe cases of exposure and has a much
broader potential application in manipulating
core body temperature to treat a variety of
ailments, including chronic disorders like cystic
fibrosis, brain damage after strokes and tumors.

One of the most unpleasant and dangerous
side-effects of extended surgery is hypothermia.
In response to anesthesia, cool temperatures and
paper-thin hospital gowns, many if not most of
the patients wheeled into the operating room
experience a drop in core body temperature.
Anesthetics usually take several minutes to wear
off, but recovery from this internal cooling can
take hours, and patients often endure chills and
shivering during this time. Recent studies have
shown that even such relatively mild hypothermia
increases infection rates and ups the frequency
of post-operative heart problems for those at
risk.

In the November issue of the Journal of
Applied Physiology, Dennis Grahn, senior
research scientist in biological sciences; John
G. Brock-Utne, professor of anesthesia; H. Craig
Heller, the Lorry I. Lokey/Business Wire
Professor of Environmental Biology at Stanford;
and Donald E. Watenpaugh, research associate in
integrative physiology at the University of North
Texas Health Science Center in Fort Worth, report
on the successful clinical trial of the rewarming
technology.

The experimental device consists of an acrylic
sleeve and mitt that fits over the hand and seals
around the patient's forearm. It contains a
water-perfusion blanket to supply heat and is
hooked to a vacuum pump to reduce the air
pressure inside the sleeve. Its design has been
patented by Stanford and licensed by Aquarius
Medical Corp. of Scottsdale, Ariz., which has
developed and is marketing a commercial version
of the rewarmer.

The device relies on the fact that the hand
and bottom of the forearm are areas of the body
specialized for the transfer of heat. They
contain an arrangement of blood vessels specially
designed for temperature regulation. Dense
networks of arteries and veins under the skin are
linked to allow blood to flow directly from one
to the other so it can act as a heating or
cooling agent.

When the body's internal temperature drops,
its automatic response is to shut down the blood
flow through these heat exchange blood vessels to
prevent more heat from escaping. While this may
help a person to survive in some conditions, it
also makes efforts to speed the warming process
slower and more difficult. The Thermo-STAT
reverses this shutdown, called vasoconstriction,
by slightly reducing the air pressure within the
sleeve. The reduced pressure causes the vessels
to open and blood to flow normally.

"This gives us the equivalent of an open
heat-pipe that leads directly to the body's
interior," says Grahn, who invented the
device and serves as a consultant to Aquarius.

The clinical trial reported in the current
paper involved 16 hypothermic patients. Ten were
equipped with the Thermo-STAT. Two were equipped
with the device operating at ambient air
pressure. The remaining four were treated using
standard techniques: Two were wrapped in warm
blankets and two had warm air blown around them.
While the standard methods warmed the patients at
a rate of about 1.4 degrees Celsius per hour, the
new rewarming method, using reduced pressure,
produced a rewarming rate of 14 degrees per hour,
a ten-fold increase.

"When we started these tests, we expected
to get maybe double the rate of rewarming,"
said Watenpaugh, who worked with Grahn in the
early stages of the concept's development.
"A ten-fold increase is really
exciting."

Grahn's concern about the problem of
hypothermia in surgery patients provided the
impetus for inventing the rewarmer. Now that it
has been developed, it has a number of other
potential applications.

One obvious extension is using it to treat
people who suffer from severe hypothermia due to
winter exposure. Hundreds of thousands of people
suffer from hypothermia annually in the United
States. The Thermo-STAT is compact, weighing only
three to four pounds, and can run on a battery,
so it is well suited for use by search-and-rescue
teams and paramedics.

In the longer term, Grahn and his colleagues
intend to explore the device's ability to
manipulate body core temperatures and how this
ability can be used to treat other diseases:

 Inducing local hypothermia may be
useful in treating chronic disorders such as
cystic fibrosis. Cystic fibrosis is caused by a
mutation of a protein found in the lungs that
prevents the protein from being processed to
maturity. Tissue culture studies indicate that
the mutated protein functions normally at
decreased temperatures. So it may be possible to
treat cystic fibrosis by periodically lowering a
patient's core body temperature.

 Much of the brain damage caused by a
stroke occurs after the initial event. According
to animal studies and limited clinical reports,
small decreases in brain temperatures can protect
the nerves from much of this damage. It may be
possible to use the Thermo-STAT in a cooling
mode, along with muscle relaxants, to decrease
brain temperature rapidly enough to reduce stroke
damage.

 Hyperthermia, an elevated core body
temperature, could be useful in the treatment of
cancer. Studies are currently under way to see if
local, regional or whole body hyperthermia ‚
induced with both external and internal heating
devices ‚ can help shrink tumors. Current
heating methods are both uncomfortable and carry
considerable risk. Adapting the Thermo-STAT could
deliver the required heating with less risk to
the patient.

Studying the effects of altering core body
temperature is a "hot" research area
right now, Grahn says. So, researchers are likely
to come up with other applications for devices of
this sort.